When is it time to change the exercise you're doing?

I've just started strength training again, and I'm wondering how to know when it's time to switch up my routine?

I've heard that once we can easily do 8-12 reps (I'm assuming that's on the 2nd or 3rd set), it's time to transition to a heavier weight. But how often should I be changing the exercise I do? And how do I know which exercise to replace it with? Same goes for cardio, I guess. How do you know when it's time to change things up?

I think 6-8 weeks is the usual for a new routine, but I'd keep the bigs in there and just mix up the rep scheme: deadlift, back squat, etc. Sorry, been doing Crossfit for a few years, and we rarely do the same workout twice, so it's hard to remember!

It's 4-6 weeks... I am now doing Group Power classes and she changes up every 6-8 weeks, by the time the 4 or 5th week comes along I am ready for a new routine, instead I increase my weights and that helps a lot... When I was weight training on my own in the gym I would change every 2 weeks because I get bored easily... But rule of thumb is 4-6 weeks...

You usually replace it with an exercise of the same muscle group... For example squats, you could replace, or add to your routine, Sumo squats... Here is a great site http://www.exrx.net/ for losts of varitions of exercises...

As for the cardio I change my routine up by adding intervals ie: HIIT, or hills, duration, etc...

For myself, I know when to change things up when I am BORED...

Hope this helps....

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